In this contribution, we present an overview of some recent research trends in the field of photonics. Topics treated in this overview include (1) what is nonlinear optics and why should we care about it? (2) implications of the ability to control the velocity of light; (3) quantum and nonlinear optical imaging; and (4) the development of new photonic
materials.

Label‐free, non‐contact, non‐destructive, on‐line (video repetition rate), high resolution, full field (no scanning), quantitative analysis of morphology and dynamic processes in living cells are required features in life science research and medical
diagnostics.
Digital Holography combined with microscopic imaging provides these features simultaneously. The modular integration of digital holographic
microscopy (DHM) into commercial microscopes yields an axial resolution with interferometric resolution while the lateral resolution is diffraction limited. As amplitude and phase are available by numerical reconstruction from a single digital hologram subsequent automated focus correction is enabled. The evaluation of quantitative digital holographic phase contrast
images permits also an effective detection of lateral object movements. Thus, 3D tracking is achieved. The applicability of DHM techniques for dynamic live cell analysis is demonstrated by results from tumor cells and human erythrocytes.

We present a femtosecond Laser Two‐Photon Polymerization (LTPP) system of large scale three‐dimensional structuring for applications in tissue engineering. The direct laser writing system enables fabrication of artificial polymeric scaffolds over a large area (up to cm in lateral size) with sub‐micrometer resolution which could find practical applications in biomedicine and surgery. Yb:KGW femtosecond laser
oscillator (Pharos, Light Conversion. Co. Ltd.) is used as an irradiation source (75 fs, 515 nm (frequency doubled), 80 MHz). The sample is mounted on wide range linear motor driven stages having 10 nm sample positioning resolution (XY—ALS130‐100, Z—ALS130‐50, Aerotech, Inc.). These stages guarantee an overall travelling range of 100 mm into X and Y directions and 50 mm in Z direction and support the linear scanning speed up to 300 mm/s. By moving the sample three‐dimensionally the position of laser focus in the photopolymer is changed and one is able to write complex 3D (three‐dimensional) structures. An illumination system and CMOS camera enables online process monitoring. Control of all equipment is automated via custom made computer software “3D‐Poli” specially designed for LTPP applications. Structures can be imported from computer aided design STereoLihography (stl) files or programmed directly. It can be used for rapid LTPP structuring in various photopolymers (SZ2080, AKRE19, PEG‐DA‐258) which are known to be suitable for bio‐applications. Microstructured scaffolds can be produced on different substrates like glass, plastic and metal. In this paper, we present microfabricated polymeric scaffolds over a large area and growing of adult rabbit myogenic stem cells on them. Obtained results show the polymeric scaffolds to be applicable for cell growth practice. It exhibit potential to use it for artificial pericardium in the experimental model in the future.

In this work we demonstrate an integrated air‐gap etalon that enables single wavelength operation and tuning ability for optofluidic dye laser. The integrated elastomeric air‐gap etalon is controlled by air pressure. The chip was fabricated with polydimethylsiloxane
(PDMS) via replica molding. It comprises a liquid waveguide and micro‐scale air‐gap mirrors providing the feedback. The lasing wavelength is chosen by the interference between two parallel PDMS‐air interfaces inside the internal tunable air‐gap etalon, of which pneumatic tuning can be realized by inflating the air‐gap etalon with compressed air. This dye laser exhibits a pumping threshold of 1.6 μJ/pulse, a lasing linewidth of 3 nm and a tuning range of 14 nm.

Fiber bottle microresonators supporting helical whispering gallery modes and exhibiting field maxima symmetrically located on either side of the neck of the bottle have been demonstrated. Channel dropping characteristics have been studied experimentally for the first time in this type of microresonator, using tapered excitation and probe fibers symmetrically placed on both sides of the bottle microresonator. Selective excitation on one side of the bottle microresonator leads to symmetrically located turning points and power localization on both sides of the bottle, leading to the potential to construct add‐drop filters.

We have developed a modified synthetic protocol for the growth of monodispersed, superparamagnetic, flower‐like colloidal
nanoclusters (CNCs) with 40–120 nm average diameters. Importantly, these are consisted of smaller iron oxide nanocrystals, also with adjustable size (12.2‐7.7 nm). We show that their optical properties can be tuned by applying an external magnetic field. Spectrophotometric measurements under these conditions reveal a diffuse reflectance maximum in the visible range, which is related to the CNCs assembly in ordered structures. The increasing field strength leads to a blue shift in the spectral weight when the size of the CNCs is above a critical diameter. The size‐dependent characteristics of the CNCs determine their magneto‐optical behavior and their potential in photonic crystal based technologies.

Sensing applications of holograms may be based on effects such as change in the spacing of the recorded fringes in a holographic
diffraction grating in the presence of an analyte so that the direction of the diffracted laser light changes, or, in the case of a white light reflection grating, the wavelength of the diffracted light changes. An example is a reflection grating which swells in the presence of atmospheric moisture to indicate relative humidity by a change is the colour of the diffracted light. These devices make use of the photopolymer’s ability to absorb moisture.

In a more versatile approach one can add inorganic nanoparticles to the photopolymer composition. These nanoparticles have refractive indices that are different from that of the bulk photopolymer. During the holographic recording of diffraction gratings, the polymerisation and accompanying diffusion processes cause redistribution of the nanoparticles enhancing the holographic
diffraction efficiency. Zeolite nanoparticles have the form of hollow cages enabling them to trap analyte molecules of appropriate sizes. The refractive index of the nanoparticle‐analyte combination is normally different from that of the nanoparticles alone and this alters the refractive index modulation of the recorded grating, leading to a change in diffraction efficiency and hence of the strength of the diffracted light signal.

Yet another approach makes use of a principle which we call dye deposition holography. The analyte is labelled using a dye which acts as a photosensitiser for the polymerisation process. When the analyte labeled is deposited on a layer containing the other photopolymer components photopolymerisation can take place. If the illumination is in the form of an interference pattern, a diffraction grating is formed, in the region where dye has been deposited. In this way the formation of a holographic
diffraction grating itself becomes a sensing action with the potential for extremely high signal to noise ratio.

The method also allows fabrication of photonic devices by direct writing, using photosensitising dye, of structures such as Fresnel zone plate lenses and waveguides onto the photopolymer layer followed by exposure to spatially uniform light.

Our work on HDS is concerned with enhancing the diffraction efficiency of user selected very weak diffraction gratings by illumination with a single beam at the Bragg angle. Light in the illuminating beam is coupled into the diffracted beam and the two interfere to enhance the grating strength. In this way grating
diffraction efficiency can be raised above a threshold so that a binary zero can be changed to binary one. A large number of identical weak holographic gratings may be multiplexed into the recording medium at the manufacturing stage, for user selection at the data recording stage. In this way consumer HDS systems could be made much more simply and cheaply than at present.

Hybrid materials, consisting of an amphiphilic block copolymer matrix incorporating metal
nanoparticles, have attracted great attention due to their unique properties, such as the catalytic behavior or the optical properties, making them potential candidates for photonic devices. High purity block copolymers, such as poly(isoprene‐b‐acrylic acid) (PI‐b‐PAA) and poly[(sodium sulfamate‐carboxylate‐isoprene)‐b‐tert‐butylstyrene] (BS‐SCI), have been synthesized by anionic polymerization and dissolved in selective solvents for the formation of well defined micelles. These block copolymers have been used as matrices for the in situ synthesis of gold nanoparticles either inside the dense core or at the periphery of the corona of their micelles. The systems were investigated by dynamic light scattering (DLS), UV‐visible and ATR‐IR spectroscopy, atomic force microscopy
(AFM) and transmission electron microscopy
(TEM). Additionally, the third non linear optical response of the hybrid materials synthesized has been investigated using the OKE and Z‐scan techniques. The optical limiting of these systems has also been investigated.

The holographic recording properties of charged zeolite containing photopolymerisable nanocomposites were studied. Photopolymer samples doped with pure silica MFI‐type zeolite
nanoparticles were charged using corona discharge. The holographic properties of the nanocomposites were characterised in real time using the Stetson geometry of recording. The influence of the type of charge—positive or negative on the dynamics of holographic recording and the final diffraction efficiency was studied.

The formation of surface relief profile in photopolymerisable systems when illuminated with a focused beam of light is simulated numerically using a two‐way diffusion
model that accounts both for monomer and short polymer chains diffusion. The concentration and spatial distribution dynamics of monomer, short and long polymer chains are calculated. It is assumed that the surface profile is a linear combination of monomer and polymer concentration with appropriate coefficients accounting for polymer shrinkage. A good agreement between the calculated and the experimentally measured profiles is observed thus demonstrating the successful application of the two way diffusion in modeling this system.

We report about preparation and application of index guiding germanium
doped
microstructured fibers, special designed for Bragg grating inscription. Due to their maximum germanium oxide concentration of 36 mol% they show a very high photosensitivity. The core diameters of the PCFs were variied between 1.6 and 6.6 μm by changing the fiber diameters. For small core PCF preparation we integrated an additional microstructured cane overcladding step. The cores are about at half total diameter doped with germanium. The holey silica
claddings are arranged in a five ring hexagonal package with a hole‐pitch ratio of about 0.9 and 0.3. So we can vary the inscription efficiency of Ge
doped PCFs. In difference to other highly doped or non‐silica PCFs with highly polarizable and probably photosensitive core components, e.g. PCFs with lanthanum glass core, germanium
doped PCFs show beside their high photosensitivity a low spectral loss. Measured with an unstructured fiber the highly germanium
doped
silica core material exhibits a minimum loss of about 6.5 dB/km. Inserted in the PCF structure the attenuation is increased to about 40 dB/km at a wavelength of 1.2 μm for the large core PCF. The small core PCF show an increased loss level in the hundred dB/km range. This effect is caused, as well as the increase of hydroxide impurification during the partial “atmospheric” PCF preparation procedure, by structural imperfections of the designed PCFs. The high germanium concentration in the central core region allows a suitable Bragg grating inscription.

We present a fiber stretcher for Chirped Pulse Amplification (CPA) based on Concatenated Chirped Fiber Bragg Gratings (CBFG) on Polarization Maintaining (PM) and Large Mode Area (LMA) fibers. Phase matching with UV‐trimming technique allows us to reduce strongly the ripples in the stretched beam.

Results are presented on the all‐optical tuning of the attenuation bands of an optical fiber long period grating utilizing a photochromic outcladding overlayer. The outcladding overlayer consists of PMMA polymer
doped with the photochromic molecule of spiropyran. The spectral transmission characteristics of the long period grating are reversibly altered using sequential exposures of 355 nm and 532 nm, Nd:YAG laser radiation. The spectra recorded refer to long period grating notch shifts and extinction ratio modification of 1.2 nm and 0.5 dB, respectively.

Multi‐section tunable lasers with optical injection are simulated using the travelling wave approach. By investigating the trajectory of the system the dynamical state can be obtained. The locking bandwidth for a large injection regime and the dynamics outside the locking bandwidth for small injection strengths are presented. It can be seen that the locking bandwidth becomes symmetric around zero detuning for high injection strengths. The dynamics outside the locking bandwidth for small injection strengths are comparable to a single‐section single‐mode semiconductor laser and it is shown that the stability map exhibits similar patterns.

In this presentation, we consider the main issues related to power scaling in fiber lasers, such as suitable pumping schemes and pump requirements, fiber designs, limiting non‐linear effects and parasitic issues like photo darkening. We review the latest developments in the field of high power fiber lasers and present some of the new emerging applications. Finally, we will consider the main challenges regarding future developments and further power scaling.

We give an overview of our studies on coherent control of extreme nonlinear optical properties via few‐cycle laser pulses with transverse distribution, which include ultrashort transient population grating as well as self‐focus effects on extreme nonlinear optics, etc.

We characterize the shift of the carrier‐envelope phase of few‐cycle pulsed Gaussian beams passing through a focus and describe two ways of slowing down the carrier‐envelope phase shift in the focal volume, as needed in phase‐sensitive, strong‐field light‐matter interactions.

By solving the full‐wave semiconductor
Maxwell‐Bloch
equations, we investigate the pulse propagation properties on resonant intersubband transitions in multiple semiconductor
quantum wells. We find that self‐induced transmission could be realized by properly adjusting the area of input pulse.

We show that there are three distinct regions corresponding to the internally produced axial parametric emissions. Namely an exponentially grown region, of the
emission, as a function of the laser peak intensity, a linear region due to mainly to the destructive quantum interference of the pump excitation and the produced emissions, and a region of complete saturation due to the considerable transfer of population to the excited states and the activation of an alternative available emission path.